Tuning quadruple surface plasmon resonance in gold nanoellipsoid with platinum coating: from ultraviolet to near infrared

The localized surface plasmon resonance (LSPR) properties of Pt-coated Au nanoellipsoid have been studied using the quasi-static calculation. Because of the Pt coating, both the transverse and longitudinal LSPR absorption peaks (denoted as AuT and AuL) corresponding to Au-Pt interface of Au nanoellipsoid get intense greatly in the visible and infrared region. Due to the longer relaxation time and higher conduction electron density, two new LSPR absorption peaks corresponding to transverse and longitudinal resonances of outer Pt shell surface (denoted as PtT and PtL) take place in the ultraviolet region. The intensity and wavelength of these four LSPR peaks are sensitive to the Pt coating thickness, and could be further fine tuned by changing the aspect ratio of inner Au nanoellipsoid and environmental dielectric constant. Thus we can obtain four intense LSPR peaks from ultraviolet to near infrared wavelength region. It is interested to find that the AuT and AuL peaks always get intense as the Pt thickness is increased. However, only on condition that environment has a small dielectric constant, the PtT and PtL peaks get intense as the Pt thickness is increased. The PtT and PtL peaks always red shift as the Pt thickness is increased. However, only on condition that environment has a large dielectric constant, the AuT and AuL peaks red shift as the Pt thickness is increased. By increasing the aspect ratio, the four LSPR peaks could be separated from each other and distribute over a wider wavelength range. These calculation results provide well potential application for multichannel plasmonic sensing.